1. Field of the Invention
The present invention relates to a vehicle lighting unit and, more particularly, a projector-type vehicle lighting unit used as a passing-beam (lower beam) headlight.
2. Background Art
Nowadays a projector-type headlight is often employed as the vehicle lighting unit. This projector-type headlight is equipped with a projection lens arranged on a lens center axis extending in the longitudinal direction of the vehicle, a light source arranged on the rear side of the rear focal point of this projection lens, and a reflector for reflecting forward a light from this light source to go toward the lens center axis.
When this projector-type headlight is used as the passing-beam headlight, a shade for shielding a part of the reflected light from the reflector to remove an upward illumination light is provided between the projection lens and the reflector. Accordingly, a passing-beam light distribution pattern having a light-shade boundary line is formed (see JP-A-2004-095481, for example).
A basic light distribution pattern for the passing-beam light distribution pattern is a light distribution pattern having a light-shade boundary line that is formed by projecting a shape of an upper end edge of the shade. In the light-shade boundary line, an opposite lane side is constructed by a horizontal cut-off line and an own lane side is constructed by an oblique cut-off line that rises leftward from the horizontal cut-off line at an angle of 15°. Also, in this basic light distribution pattern, a hot zone (high luminous intensity area) is formed under and near the right end portion of the oblique cut-off line of the light-shade boundary line.
However, in the above projector-type headlight in the background art, normally a focal position of the projection lens is set to the upper end edge of the shade during the passing-beam light distribution. Therefore, an almost half of the upward illumination light is removed by the shade, and particularly a part of the hot zone is cut by the oblique cut-off line of the light-shade boundary line. As a result, such a problem existed that a utility factor of the light is low. Also, there are some shades to which a mirror process has not been applied. In this case, a loss due to a reflection not a little occurs.